In certain operations involving automated machines for drilling, boring and other operations, it is desirable to be able to control and predetermine the depth of a cut or bore hole in the workpiece, independently of the position of the control machine which advances the cutting tool.
Conventionally, this type of boring operation has been accomplished through the use of servo motor feed packs and gaging stations with feedback controls.
Typical of the prior art is U.S. Pat. No. 4,530,625 issued Jul. 23, 1985 to Corley et al., and U.S. Pat. No. 4,273,481, issued Jun. 16, 1981, also to Corley et al. Both of these prior patents utilize a spindle stop arrangement which is axially slidable with respect to the cutting bit, and which is such as to relieve hydraulic pressure utilized to drive the cutting tool into the workpiece, when the cutting bit has reached a given, predetermined depth. This is accomplished by uncovering a hydraulic passageway, or by unseating the ball of a check valve. Unfortunately, constructions of this type are not capable of depth tolerances as small as 0.001 inches.
Another patent of peripheral interest is U.S. Pat. No. 3,516,327, issued Jun. 23, 1970 to Wilson.